Multi-layer compositions for cosmetic use are well known in the prior art, particularly in the area of cleansers and make-up removers. A multi-layer composition formed with separate oil, alcohol and water layers will often comprise compounds that are incompatible with each other. The different layers are typically separate when at rest, and form an emulsion when agitated. This way the incompatible compounds are kept separate until the time of use of the cosmetic. In addition to enabling the presence of different incompatible compounds, such multi-layer compositions are typically visually appealing and provide an interactive experience for a user.
Most multi-layer products currently on the market are formed with two layers, typically a top oil layer and a bottom aqueous layer that comprises skin care actives, such as humectants, glycols, preservatives, alcohol, salt and water. One or more surfactants are typically provided in either the oil or the aqueous layer to facilitate quick homogenization of the two layers before use. After use and when left to rest, the composition separates back into two distinct layers over a period of hours.
For multi-layer compositions where quicker separation is required, the amount of surfactant may be reduced or eliminated completely. Where no surfactant is provided, the layers will separate immediately after a user stops agitating the composition. This is generally acceptable for cosmetic cleansers, however, for other skin care products (such as moisturizers), it is important to retain the correct ratio of oil to aqueous phase in the homogenized product during application to ensure consistent efficacy and sensory benefits throughout the product usage.
Most multi-layer compositions currently on the market have an oil layer formed mainly, if not entirely, of synthetic oils. Synthetic oils tend to have a purer chemical form than natural oils which make them more predictable and easier to incorporate in different forms of product, such as multi-layer compositions. Replacement of synthetic oils with natural oil(s) in existing multi-layer compositions can significantly compromise the aesthetic benefit currently associated with such products. In this respect, natural oils tend to contain carry over ingredients, such as saponin, that are known to take on a soap-like form when shaken with water. This soap-like form becomes more noticeable, and remains present longer in the presence of a surfactant due to the cumulative foaming effect of the surfactant together with the carry over ingredient. This can lead to the formation of a milky layer at the meeting point between the oil layer and the aqueous layer that may take some time to dissipate.
Surfactants are known to have additional disadvantages of use, such as causing skin irritation by disturbing the skin structure. Furthermore, they may attract oil ingredients into the aqueous phase during storage and transport and vice versa. Thus there is a need to form multi-layer compositions that do not suffer from some of these issues associated with use of a surfactant.
U.S. Pat. No. 7,988,981 discloses a multi-layer composition including an oil layer formed of a mixture of mineral, vegetable and synthetic oils, and an aqueous layer comprising at least one polyol and water soluble salts. U.S. Pat. No. 7,988,981 avoids the negative effects of using a surfactant with natural oils, but this instead leads to a multi-layer composition that, upon agitation, forms a homogenous mixture that separates out again immediately when it is left to rest.
Thus, there is still a need to improve existing multi-layer compositions to provide greater flexibility of choice of ingredients and better control of separation time.